The present invention relates to the fabrication of thin film heads for data storage systems. More particularly, the invention relates to the deposition of a nickel seed layer adjacent to the magnetic core of a thin film magnetic head, to reduce the effects of read instability.
Thin film magnetic read/write heads are used for magnetically reading and writing information on a magnetic storage medium which moves relative to the head, such as a magnetic disc. A thin film magnetic head comprises a pair of "yokes" and "poles" which form the magnetic core of the head. Electrical conductors (or coils) pass between the core and are used for both reading and writing information onto the magnetic storage medium. During a write operation, electrical current is caused to flow through the coils generating a magnetic field in the core. A gap region occupies a small space between two pole tips of the magnetic core. The write current in the coils causes magnetic flux to span the gap region. This magnetic flux is then used to impress a magnetic field upon a storage medium producing a magnetic transition, which is then recorded. During the read operation, the magnetic head and the storage medium also move relative to one another, causing magnetic flux to link through the coils. Electrical signals in the coils may be sensed with electric circuitry which enable the recovery of information stored on the magnetic medium.
In thin film heads, the magnetic core serves as a link between the magnetic flux emanating from the transitions in the recording medium and the coils. In doing so, the magnetization of the core changes to reflect signal flux variations. The changing magnetic state of the core is characterized by either magnetic rotation or domain wall motion. In some cases, excitation of the write signal can cause domain walls in the core to move irreversibly.
During the demagnetization process, (i.e. after the termination of a write current pulse), the core may be left with undesirable domain patterns. More particularly, the core may be unable to relax back to a stable magnetic state. For readback, a stable magnetic state exists when the magnetic domains are oriented in an easy axis direction. Particular domain patterns, such as vertical walls in the pole tip region, are associated with a high degree of magnetic instability during the readback. The inability of a magnetic head to return to a stable relaxed state may be caused by defects such as scratches, local stresses caused by the deposition process, or inhomogeneities in composition of the core material in the head. In any case, if the domain patterns of the head vary significantly from the "desirable" relaxed magnetization state, the performance of the head is compromised.
One way in which the performance of a thin film magnetic head is degraded is by the effects associated with read instability. One effect of read instability is "head wiggle", which is a distortion of the read signal. The distortion primarily appears as noise on the trailing edge of the readback signal.
European Patent Publication No. 0301823 and IBM Technical Disclosure Bulletin, vol. 35, no. 1B, June 1992, pages 457-459, "Laminated Seed Layers for Plated Thin Film Heads and Structures" describes thin film magnetic heads employing Ni-Fe alloy thin films. European Patent Publication No. 0387143 describes a thin film magnetic head employing Ni-Si thin films. The Journal of Applied Physics, vol. 64, no. 1, August 1988, pages 1343-1346, "Magnetic Anisotropy in Ni/Fe Artificial Lattice Films" describes some of the magnetic properties of laminated Ni and Fe composite films and suggests that such laminated films could be used to form a magnetic yoke in a thin film magnetic head. None of these documents addresses the problem of read instability.
The occurrence of head wiggle causes incorrect data to be retrieved from the magnetic medium. The prior art does not adequately compensate for the effects of read instability in both the design and properties of material used in thin film head fabrication. An improved then film head in which the effects of read instability are consistently reduced, would be a significant improvement to the art.